Staffers on board Thursday's Air Canada flight from Los Angeles to Toronto reported a popping sound just before the pilot began a deliberate descent - the start of a long and often stomach-churning ordeal for everyone on board.

The flight had just left Los Angeles around noon when the plane, which had been flying at about 12,000 metres, descended to just 3,962 metres and began circling above the Las Vegas airport.

The Airbus A-320 circled for hours above the sweltering desert as passengers were forced to endure often severe turbulence caused by the heat rising off the mountains.

One McGuinty staffer described the trip as a roller-coaster ride that left roughly one-third of the people on the plane making use of their air-sickness bags. Some had shortness of breath as a result of the altitude and loss of cabin pressure.

"We circled for two-and-a-half hours in order to burn up fuel before we could land," McGuinty said just a few hours after arriving in Toronto.

"We were fuelled up to get to Toronto, and we wanted to land urgently in Las Vegas, so we just flew over the desert."

Air Canada spokesman Peter Fitzpatrick said the 136 passengers were never in any imminent danger.

It was ultimately a problem with the air conditioner, which Fitzpatrick said doesn't just cool the plane, but also plays a role in maintaining cabin pressure.

Nobody was injured as a result and crew members followed proper procedure, he added.

"It's something that could be fixed and it wasn't an issue of compromising the safety of the aircraft," Fitzpatrick said.

"I think it was just a matter of one of the air conditioners malfunctioning so they pulled over as quickly as they could to try and get it fixed for the comfort of the passengers."

Calling it an "adventure," McGuinty played down the seriousness of the incident Friday.

"I had confidence in the crew. They were very professional and handled themselves very well," he said. "All's well that ends well, as they say."

Staff members described the mood as "tense," and said the crew wasn't immediately forthcoming about how long it would take to land or about what was happening.

The aircraft is expected to be repaired and put back into service.

Once McGuinty's plane landed in Las Vegas, the premier posed for pictures with the crew before he was introduced to tennis great Andre Agassi in the Las Vegas airport lounge.

A staffer said the premier asked him about the school he founded for high risk kids in Las Vegas.

The flight finally left Vegas around 10:30 p.m. local time and arrived in Toronto around 6 a.m., just four hours before Friday's swearing-in ceremony to formalize a modest cabinet shuffle.

Fitzpatrick said the incident was much different than one in January that sent 10 people to hospital with injuries.

While that Air Canada flight from Victoria to Toronto is still under investigation, reports at the time suggested a computer malfunction sent the jet tossing and turning.

Passengers and dishes were thrown about the plane causing a number of minor injuries.

Last fall, nine people were hurt when a Halifax-bound WestJet flight hit unexpected turbulence.

The aircraft dropped 20 metres and those who weren't buckled in were lifted right out of their seats.